In a container molding process affected via the action of pressure due to blowing, the pre-molded elements comprised of a thermoplastic material, e.g. pre-molded elements comprised of PET (Poly(ethylene terephthalate)), are forwarded to various processing stations inside a blowing machine. Typically, such a blowing machine has a heating device as well as a blowing device, whereby the pre-molded element, which has been regulated thermostatically beforehand, is expanded, by means of biaxial orientation, to produce a container in the region of the blowing device. Expansion takes place with the help of compressed air that is introduced into the pre-molded element that is to be expanded. The technical process in the case of such an expansion of the pre-molded element is explained in DE-OS 43 40 291.
The basic structure of a blowing station for use in molding containers is described in DE-OS 42 12 583. Possibilities for thermostatically regulating the pre-molded elements are explained in DE-OS 23 52 926.
The pre-molded elements and the blown containers can be transported within the blow-molding device by use of various handling devices. The use of transportation mandrels, on which the pre-molded elements are positioned, has proven especially valuable in practice. However, the pre-molded elements can also be handled by use of other supporting devices. Available constructions also include the use of grappling tongs for handling the pre-molded elements, and the use of expansion mandrels, which can be introduced into an opening region of the pre-molded element for supporting purposes.
The handling of the pre-molded elements explained above is effected, on the one hand, using the so-called two-stage process, in which the pre-molded elements are first manufactured in an injection molding process, and then are stored on an interim basis; it is only later that they are conditioned, in terms of their thermostatically regulated temperature, and inflated to produce a container. On the other hand, use is also made of the so-called one-stage process, in which the pre-molded elements are suitably thermostatically regulated immediately following their manufacture, by means of injection molding technology, and adequate solidification, after which they are inflated.
Various embodiments of blowing stations that are used are known. In the case of blowing stations that are arranged on rotating transport wheels, the ability of the mold supports to be opened on a hinge in a book-like manner is frequently encountered. However, it is also possible to use mold supports that can be moved relative to one another, or that are guided in a different manner. In the case of spatially fixed blowing stations, which are especially well suited for housing several cavities for container molding purposes, plates, which are typically arranged parallel to one another, are used as mold supports.
In addition to the two blow mold segments, a conventional blow mold includes a base extension that is capable of being positioned. Such a base extension is required when undercuts occur in a horizontal direction in the base region of the container that is to be manufactured. After the container has been molded, the base extension is raised, and the two blow mold segments are separated from one another in order to allow the blown container to be extracted from the blowing station. The base extension is usually screw-fitted to a base plate. In addition, screw connections are provided in order connect cooling water channels inside the base extension to suitable supply lines.
In the event of a product change, it is necessary to change both the blow mold segments and the base extension in order to generate the container contours for the new product. The corresponding change of the base extension is relatively labor intensive because of the screw fitting that is provided for the base extension and the base plate, along with the screw fittings for the connections for the cooling medium.